1. Field of the Disclosure
The disclosure relates to a vehicle frame, in particular to a bicycle frame for mountain bikes or trekking bicycles.
2. Discussion of the Background Art
In particular with bicycles used under riding conditions that vary extremely, such as mountain bikes or trekking bicycles, it is common to provide a sprung rear frame, i.e. a rear frame that is pivotably connected with a main frame element. With such a frame, the main frame element is formed by a top tube, a down tube and a seat tube, while other frame geometries are conceivable. Under varying riding conditions, ranging from steep downhill slopes to steep uphill slopes, the load distribution between the front wheel and the rear wheel changes drastically. When riding on plane ground, about 70% of the weight force act on the rear wheel and only 30% act on the front wheel. On the other hand, when riding uphill, almost 100% of the weight act on the rear wheel so that the front wheel might even be lifted slightly off the ground. Similarly, when riding down steep slopes, it may happen that almost 100% of the weight are borne by the front wheel so that a lift-off of the rear wheel may occur.
With bicycles, such as mountain bikes, which comprise a damping element for damping the movement of the rear frame, the damping element is adjusted in such a manner that about 20-30% of the spring travel are provided as negative spring travel. This means that, given a static load by the weight of a driver, the damping element is compressed for about 20-30% of the total spring travel. Thereby, the rear frame will rebound when riding over uneven ground, such as over holes or the like. Comfort and traction are thereby improved. When riding uphill, such an adjustment of the negative spring travel results in an acute seat angle and thereby causes a displacement of the sitting position of the driver towards the rear wheel. This causes the front wheel to lift off even at rather gentle ascending slopes. Moreover, the frame is sensitive to driving influences. Driving influences can be suppressed by adjusting the compression damping, whereby, however, energy is converted into heat so that the power of the driver is not fully used to move the bicycle. Further, suppressing the driving influences does not cause a change in geometry so that the same is still unfavorable for riding uphill. Alternatively, an adjustment of the air pressure in the damping element could be made when riding uphill, with the air pressure having to be increased during a ride uphill. However, this means a considerable effort.
From U.S. Pat. No. 7,712,757, a mountain bike frame is known which comprises a main frame element and a rear frame connected with the same in an articulated manner. A damper element is pivotably connected with the rear frame at a first or upper connection point via a first rocker link. The lower or second connection point of the damper element is pivotably connected with the down tube via an intermediate element. The intermediate element or a second rocker link carries the main link bearing, i.e. the link bearing of the rear frame. Thus, the main link bearing is not connected directly with the main frame element, but is connected therewith only indirectly via the connection element.
Further, the structure described in U.S. Pat. No. 7,712,757 is provided with a spring element arranged between the connection element and the seat tube, by which spring element the lower or second connection point of the damper element can be shifted. Here, the second connection point is shifted automatically depending on the tension of the chain. The dependence of the damping behavior on the chain tension is often perceived by cyclists as being objectionable. This is true in particular when riding off-road when the rear frame moves rather frequently and strongly. Further, the stiffness of the frame is reduced by the displacement of the main link bearing into a moving damping element. Moreover, the solution described in U.S. Pat. No. 7,712,757 has the disadvantage that the overall weight of the frame is drastically increased thereby. Further, the solution described in U.S. Pat. No. 7,712,757 requires to significantly shift the lower or second connection point of the damping element to achieve a relevant influence on the damping effect or a relevant change of the damping or spring characteristic. As a result the components have to be accordingly solid, since displacements by more than 40 mm to 50 mm are required. Further, the connection element and the displacing element in the form of a spring have to guarantee the absorption of substantial forces so that a solid design of these components is required for this reason, too, whereby the overall weight of the frame is increased.
In the interest of hanging the frame geometry, it is further known from U.S. Pat. No. 6,877,591 to change the position of the second connection point connected with the main frame element. The second connection point is connected with the down tube via a fixing element and can be fixed in different positions. The connection position can be changed only by loosening the connection point using tools. Thus, changing the position of the second connection point is rather troublesome and, in particular, is impossible to accomplish while riding.
Further, an arrangement of a damping element between a sprung rear frame and the main frame element is known from GB 2 360 497. Here, the first connection point of the damping element with the rear frame is not formed by a rocker link connected with the main frame element, but is realized in an immediate manner. The second connection point of the damping element fixedly connected with the main frame element. For a change of the frame geometry, the first connection point may be shifted within a guiding slot. Again, this is a frame geometry that can be changed only with effort using tools and, in particular, cannot be varied while riding.
It is an object of the disclosure to provide a bicycle frame, in particular for mountain bikes and trekking bicycles that can be adapted to different riding situations in a simple manner.